The present invention relates to information storage devices. More specifically, the present invention relates to a Magnetic Random Access Memory (“MRAM”) device.
Consider the example of an M RAM device including a resistive cross point array of spin dependent tunneling (SDT) junctions, word lines extending along rows of the SDT junctions, and bit lines extending along columns of the SDT junctions. Each SDT junction is located at a cross point of a word line and a bit line. The magnetization of each SDT junction assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of ‘0’ and ‘1.’ The magnetization orientation, in turn, affects the resistance of the SDT junction. Resistance of the SDT junction is a first value (R) if the magnetization orientation is parallel and a second value (R+ΔR) if the magnetization orientation is anti-parallel. The magnetization orientation of the SDT junction and, therefore, its logic value may be read by sensing its resistance state.
A write operation on a selected SDT junction is performed by supplying write currents to the word and bit lines crossing the selected SDT junction. The currents create two external magnetic fields that, when combined, switch the magnetization orientation of the selected SDT junction from parallel to anti-parallel or vice versa.
Too small a write current might not cause the selected SDT junction to change its magnetization orientation. In theory, both external fields combined should be sufficient to flip the magnetization orientation of the selected SDT junction. In practice, however, the combined magnetic fields do not always flip the magnetization orientation. If the magnetization orientation of the selected SDT junction is not flipped, a write error is made and an increased burden on error code correction can result.
SDT junctions that see only one magnetic field (that is, SDT junctions along either a selected word line or a selected bit line) are “half-selected.” In theory, a single magnetic field should not flip the magnetization orientation of an SDT junction. In practice, however, the magnetization orientation can be flipped by a single magnetic field. If the magnetization orientation of a half-selected SDT junction is flipped, an undesirable erasure occurs and an increased burden on error code correction can result.
There is a need to improve the reliability of writing to SDT junctions. More generally, there is a need to improve the reliability of writing to magnetic memory elements of MRAM devices.